The present invention relates to atherectomy devices, in general and in particular to brake systems for use in atherectomy devices.
Arteriosclerosis is a common vascular disease in which a patient""s blood vessels become hardened and blocked by plaque or clots that impede blood flow. Left untreated, this condition is a major contributing factor to the occurrence of high blood pressure, strokes and cardiac arrest.
To treat arteriosclerosis, many invasive and non-invasive techniques have been developed. For example, cardiac bypass surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is fairly traumatic because the entire chest cavity must be opened to access the occluded vessel. Therefore, the procedure is not generally performed on elderly or relatively frail patients.
One example of a minimally invasive technique that is being performed on a greater number of patients is to remove the occluding material from a patient""s vessel with an atherectomy device. To perform this procedure, a guide catheter is typically inserted into the patient""s femoral artery and advanced until the distal end of the guide catheter is located in the patient""s ostium. A guide wire is then inserted through the guide catheter and traversed into the coronary arteries and past the occluded material to be treated. Then, as described in U.S. Pat. No. 4,990,134, issued to Auth, an atherectomy catheter having a small abrasive burr is advanced through the guide catheter and over the guide wire to the point of the occlusion. The burr is then rotated at high speed and passed through the occlusion during an ablation phase in order to remove particles that are sufficiently small such that they will not reembolize in the distal vasculature. As the burr removes the occlusion, a larger lumen is created in the vessel and blood flow is restored.
During the atherectomy procedure, after the burr has been routed over the guide wire to the location of the occlusion, the physician activates a rotational source (i.e. gas turbine) coupled to the burr by depressing a foot pedal so that the rotational source spins the ablation burr up to operational speed. In a conventional atherectomy device, a brake system is activated in unison with the rotational source to prevent rotation of the guide wire during the ablation phase of the atherectomy procedure. If the guide wire is not secured, the rotational inertia of the burr may begin to spin the guide wire and advance it downstream of the occlusion.
As shown in FIGS. 1 and 2A, a conventional brake system 20 consists of a brake cylinder 22, having a bore 24 extending therethrough. The cylinder 22 is mounted to a brake assembly bracket 26. A cylindrical piston 28 having an inner tapering or partially conical bore 30 linearly reciprocates within the bore 24 of the brake cylinder 22. A wiper ring seal 32 is seated on a front surface 34 of the piston 28 to create a chamber 38 within the bore 24. A cylindrically shaped brake collet 40 is disposed adjacent to the rear surface of the piston 28. The brake collet 40 includes an axial bore 46 for allowing the guide wire 42 to extend therethrough.
Referring to FIG. 2A-2B, the distal end of brake collet 40 further includes a pair of tapered jaws 44 that begin at approximately the mid point of the brake collet 40. The tapered jaws 44 have a conical engagement surface 50 that mates with the tapering bore 30 of the piston 28. The jaws 44 are separated by a slot 52 that extends from the distal end of the brake collet 40 toward the mid-section such that the jaws are hinged at the proximal end but can bend inward toward the exposed guide wire 42 when the jaws are forced into the tapering bore 30 of the piston 28.
The brake cylinder 22 has a gas inlet 56 that connects the chamber 38 to a source of gas through a gas conduit 58. Attached to one end of the brake cylinder 22 is a brake bracket 60. The brake bracket 60 has a centrally located bore 62 to retain the distal end of the brake collet 40 and to retain the brake collet 40 in proper alignment with the piston 28. Disposed around the brake collet 40 is a return spring 64 which exerts force on the rear face 66 of the piston 28 in order to return the piston 28 to its original location after the brake system 20 is deactivated.
With reference to FIGS. 1 and 2A, during the operation of the atherectomy device, the physician rotates the ablation burr via activation of a foot pedal. Depression of the foot pedal allows gas from a gas line 70 to enter manifold 74 having a gas conduit 58 fluidly connected to brake cylinder 22, and an outlet port 78 leading to the rotation source through tube 80. Gas entering chamber 38 through gas inlet 56 exerts pressure on the front piston face 68 thereby causing the piston 28 to linearly translate within the bore 24 of the brake cylinder 22. As the piston 28 moves linearly toward the brake bracket 60, the inner tapering bore 30 of the piston 28 engages the correspondingly conical engagement surface 50 of the brake collet 40 to urge the jaws 44 radially inward to engage with the guide wire 42. The jaws 44 of brake collet 40 clamp down onto the guide wire 42 so that the guide wire 42 is prevented from rotating. After the occlusion has been ablated, the physician releases pressure on the foot pedal to deactivate the ablation burr. When the physician releases the foot pedal, the gas is shut off from the chamber 38 allowing the biasing force of the return spring 64 to move the piston 28 linearly back toward the proximal end of the brake cylinder 22 as the gas escapes back through the gas conduit 58. This disengages the brake collet 40 from the guide wire 42. To prevent potential rotation of the guide wire, care must be taken to ensure that the driveshaft has stopped rotating before the spring 64 pushes the piston 28 towards the brake cylinder 22 thereby releasing the guide wire.
While the brake system illustrated in FIGS. 1 and 2A works well to prevent rotation of the driveshaft during the ablation procedure, the present invention seeks to improve the performance and to simplify the design by eliminating the wiper ring seal 32.
The present invention is a brake activator system comprising several linear actuators using a bellows design to decrease the leakage of gas in the brake cylinder and ensure that the guide wire is prevented from rotating during the activation and deactivation of the atherectomy device.
In one embodiment, the brake activator system comprises a housing which includes two coaxially disposed apertures for receiving a guide wire therethrough. At least one bellows is coupled to the linear actuator. A brake collet having a camming surface and a braking surface is engageable with the guide wire. Expansion of the bellows urges the braking surface of the brake collet toward the guide wire to prevent the rotation thereof.
In another embodiment, the linear actuator uses two concentrically arranged bellows to form an annular chamber. Expansion of the chamber linearly translates the rear plate of the linear actuator into engagement with a brake collet. The conical shape of each engagement surface results in the brake collet clamping down on the guide wire and thus preventing its rotation.
In yet another embodiment, the brake activator comprises a housing, a pair of bellows and a pair of brake shoes. One end of each bellows is secured to opposing interior walls of the housing. Brake shoes are attached to the other end of each bellows to form two chambers. Expansion of the chambers linearly translates the brake shoes radially inward into engagement with the guide wire to prevent its rotation.
As will be readily appreciated from the foregoing description, the present invention provides a brake activator system that eliminates the use of a sliding seal commonly used in conventional designs so that the brake activation pressure bleeds down slower, resulting in a tighter grip around the guide wire during activation of the brake. Additionally, slower bleed down provides a longer period of time for the ablation burr to stop rotating during deactivation of the brake system prior to the brake tube disengaging from the guide wire.